My 11 year old cocker has had bad teeth and now had many teeth removed. Over this time he's has become very growly and snarling to the point that I can't stroke or touch him. Even talking to him will see his head go down, growling starts and he turns around slowly, moves away with his tail tucked under him. He then barks and howls for a time. He was such a lovely affectionate Spaniel and I would love to have him back, it's very upsetting to see him like this. Can this behaviour be unlearned? Any help grateful, I don't know where to start.